Ants (Hymenoptera: Formicidae) and trophobiont leafhopper nymphs (Hemiptera: Cicadellidae) become more abundant in shaded conditions: Implications for mutualism

Abstract

Abiotic factors have dramatic effects on herbivore insect populations. However, little is known about the effects of the abiotic factor of shade on the mutualism between ants and Hemiptera (aphids, scales, mealy bugs, whiteflies, treehoppers, leafhoppers). The trophobiont leafhopper Dalbulus quinquenotatus DeLong & Nault (Hemiptera: Cicadellidae) is obligatorily tended by the ant Brachymyrmex obscurior Forel (Hymenoptera: Formicidae) on the basal leaves of gamagrass Tripsacum dactyloides L. (Poales: Poaceae). To better understand the effect of abiotic factors on this relationship, we conducted a comparative experiment to investigate the abundance of ants and leafhoppers (nymphs and adults) under shaded and full-sunlight conditions. We observed mutualism between D. quinquenotatus and B. obscurior on both shaded and non-shaded gamagrasses. Nevertheless, the greatest number of B. obscurior were found tending the greatest number of D. quinquenotatus on shaded T. dactyloides. Most of these leafhoppers were nymphs. Nymphs were observed in clusters on the basal leaves. On the other hand, ant-tended D. quinquenotatus adults were observed at similar frequencies on shaded and non-shaded gamagrasses. The adults were also seen on the basal leaves and produced honeydew, but were more mobile than the nymphs. Our results highlight the importance of abiotic factors in mutualism as well as the complex interaction between shaded plants, immature leafhoppers, and tending ants.